Increasingly, routers are offloading the computationally intensive selection of paths to other network devices, referred to as path computation elements (PCEs). A PCE establishes PCE communication protocol (PCEP) sessions with one or more path computation clients (PCCs) through a network. Path computation clients, such as routers, and PCEs communicate over these PCEP sessions. A PCE may be stateless or stateful. In general, a stateless PCE does not maintain state describing TE LSPs in the network, while a stateful PCE maintains state for a subset of TE LSPs in the network. A stateful PCe may thereby utilize more sophisticated LSP path computation algorithms in some instances.
There may be two basic modes of operation for a PCE. The first mode of operation allows the PCCs to issue path computation requests to the PCE using their respective PCEP sessions. The PCE applies constraints provided in a path computation request to compute the path of a traffic engineering multi-protocol label switching (MPLS) label switched path (LSP) (which is often denoted as a “TE LSP”) through a path computation domain that satisfies the constraints. The PCE then returns the path to the requesting PCC, effectively augmenting the network path computation functionality. A PCE may be stateless or stateful. In general, a stateless PCE does not maintain state describing TE LSPs in the network. A stateful PCE, on the other hand, maintains state for a subset of TE LSPs in the network, allowing the stateful PCE to utilize more sophisticated LSP path computation algorithms in some instances.